While using my BB Classic the screen will just randomly start flashing black (Max 18 times) before it locks.

If I lock it just as it happens and wait 30 seconds then I can use the phone like normal for a bit before it starts flashing black again. While the screen is unusable I still recieve notfications, calls, and the light at the top still flashes.

When I reboot it the Blackberry|Classic words never go off, but when it get to the % of booting up then it goes black again until its done.

You can try wiping it and reloading the OS but I doubt that will fix anything. Just easy to rule out. It's almost certainly a hardware related issue in which case you'll need to consider your replacement options. eg: Warranty, Insurance, Carrier exchange, etc.